Ultra high frequency device



Dec. 3, 1940. 1

Fi e. 2.

ULTRA HIGH FREQUENCY DEVICE Original Filed Jan. 29, 19258 R. M. SMITH 2Sheets-Shet 2 (Asa/11,770

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3 wentor Boyer-5 J'mzth Patented Dec. 3, 1940 UNITED STATES PATENTOFFICE to Radio Corporation of Delaware of America, a corporationOriginal application January 29, 1938, Serial No.

Divided and this application Septemher 6, 1939, Serial No. 293,624

6 Claims.

My invention relates to ultra high frequency devices, and especially tomeans for tuning ultra high frequency devices whereby undesiredreactances may be neutralized.

This application is a division of my copending application Serial No.187,607, filed January 29, 1938, entitled Ultra high frequency devices.

In radio circuits operated at frequencies up to thirty megacycles persecond the capacitors and inductors used for tuning are usually of thelumped or concentrated type. For example, conventional electricalcondensers and solenoid types of inductors are used from the lowestradio frequencies and up to frequencies of the order of thirtymegacycles per second. At frequencies approaching five hundredmegacycles per second and upward transmission lines of the two wire orconcentric type are used as resonant circuits.

When transmission lines and associated thermionic tubes are used atultra high frequencies, the input impedance of the tubes has animportant effect on the results obtainable. It is well known that theelectrons moving from cathode to anode through the grid electrode of athermionic tube, while of slight or negligible effect at low frequency,cause a very substantial reduction of input impedance at the ultra highfrequencies. The natural capacity between the cathode and gridelectrodes, as well as electrode leads having appreciable length, whileeffecting slight reactance at low frequencies, offer large reactiveeffects at the ultra high frequencies.

The net effect of the input resistance and input reactance of thermionictubes operated at the ultra high frequencies is to establish phaseshifts which are often large enough to have adverse effects on the tubesas amplifiers. I have found that similar effects in the anode or outputcircuits account for an actual attenuation of signal frequency currentsinstead of an expected gain. These efiects may be overcome by suitabletuning adjustments, provided the tuning elements are designed so thatthe connecting leads offer negligible reactance.

In practice a real problem is presented in the elimination of theeifects of connecting leads. One might assume that a capacitor couldalways be connected to by-pass the ultra high frequency currents. torusually simply shifts the problem from the original leads to the leadsof the capacitor itself. The importance of thelead lengths atfive'hunred megacycles per second can be illustrated by stating that agrounded lea-d fifteen centimeters longstanding in space will haveminimum However, the use of a by-pass capaciimpedance at the groundedend and maximum impedance at the free end. Obviously, intermediate leadlengths will have intermediate impedances.

My invention has for one of its objects the 5 provision of means foreliminating the effects of lead lengths in ultra high frequencycircuits. Another object is to provide means for eliminating thereactive effects of the interelectrode capacities within a thermionictube. Another ob- 10 ject is to provide means for tuning thetransmission lines associated with ultra high frequency thermionictubes. An additional object is to provide means forefilcientlyconverting currents of ultra high frequency to currents of intermedi- 5ate frequency. A further object is to provide means for preventingsustained blocking of an ultra high frequency receiver by theapplication of signals of large amplitude.

My invention is described by reference to the 90 accompanying drawingsin which Figure 1 is a schematic circuit diagram of a radio frequencyamplifier, local oscillator and first detector;

Figure 2 is a sectional view of one embodiment 25 of my invention; and

Figure 3 is a sectional view of an oscillator which may be used inconjunction with the apparatus of Fig. 2.

Referring to Fig. 1, which is a diagrammatic circuit used for purposesof illustration only,

a transmission line I is connected by a matching transformer 3 to theinput of a thermionic amplifier 5. The input circuit of the amplifierincludes a resistor 1 and a capacitor 9 which prevent overloading orblocking on application of signal currents of large amplitude. Theoutput circuit of the amplifier includes an adjustable inductor H, abypass capacitor [3 and a coupling capacitor 15. 40

The coupling capacitor I5 is connected to a pair of resonant coupledcircuits ll, l9 which are grounded. The second resonant circuit l9 ismutually coupled to a local oscillator 2|. The second resonant circuitis also connected to a first detector or mixing tube 23. The input ofthe detector includes an adjustable inductor 25. The output of the firstdetector includes a network 21 which is preferably tuned to intermediatefrequency currents and which is connected to an intermediate frequencyamplifier and second detector. The intermediate frequency amplifier andsecond detector are not illustrated because they are not essential partsof my invention and they are well known to those skilled in the art.

It should be understood that the thermionic tubes of the foregoingcircuit are energized by application of suitable anode, screen, andheater currents. Likewise, the grid electrodes may be biased negativelywith respect to cathodes by self-biasing means, biasing batteries or thelike. Bypass capacitors are shown as applied in the conventional manner.While the schematic diagram shows the inductors, and capacitors asconventional elements, such showing is for the purpose of illustrationonly.

For the practical application of my invention reference is made to Fig.2 in which the line 29 represents the inner conductor of a concentrictransmission line, which is terminated by a coupling or matchingtransformer 3| of the concentric line type. The inner conductor 33 isinductively coupled to the grid connection 35 of the radio frequencyamplifier 31 and is terminated by grounding on the outer conductor ofthe transformer. The input circuit to the amplifier 31, which includesthe leads and electrodes within the thermionic tube, is arranged asfollows: The amplifier tube is mounted on a plate 39 which is locatedwithin a metal housing 4|. A metal tubular member 43 is adjustablymounted within a boss 95 in the housing. The tubular member may becapped by an insulated plug 41. At the lower end. of the tubular membera bypass capacitor is formed by insulating, with Styrol or the like, ametal plug 49 from the tubular member. The capacity of this condenser ispurposely made small so that sustained blocking will not occur whensignals of large amplitude cause grid ourrent to fiow. A resistor 5| isconnected between the plug 69 and the tubular member 43. A rod 53 isslidably mounted within the plug, and fixedly connected to the gridelectrode of the amplifier 31 by a suitable clamp 55.

The tubular member 43 may be moved up and down in the boss to therebyadjust the length of the circuit between the grid electrode and thebypass capacitor formed by 49, etc. The inductive reactance of thiscircuit is adjusted to substantially neutralize the capacitive reactanceof the amplifier input. It should be recognized that the leads andelectrodes within the amplifier are a part of the resonant circuit. Itwill be observed that the capacitance of the bypass capacitor remainsfixed. To insure that the junction of the bypass capacitor and thehousing shall be grounded at a point of suitable impedance, the rod 35is concentrically extended within the tubular member -13 and terminatedby a sliding concentric tube 51. This supplemental grounding circuit isrequired because of the relatively small capacity of the bypasscondenser.

If the ground connection is to be made of low impedance, the slidabletube 5! is adjusted so that the rod 53 and tube 51 have an effectivelength of one quarter wave measured from the ground point toward thehigh potential end of the system. If the ground termination is to beterminated by a high impedance for any reason, the effective lengthshould be a half-wave. I prefer the quarter wave adjustment in thepresent circuit. Thus arranged the amplifier input circuit may be madeto resonate at the operating frequency and the bypass capacitor andresistor 5| have leads of negligible length, if they can be said to haveany leads at all. The capacitor and resistor described immediately abovecorrespond respectively with the elements 9 and of Fig. 1. The balanceof the amplifier input circuit corresponds to the transformer 3 of Fig.1.

The output circuit of the amplifier 3'! is as follows: The anode isconnected to a plate 59 which is separated by an insulator 6| from aquarter wave line hereinafter described. The anode is also connected,through a conductor 63 of adjustable length, to the positive terminal ofa B- battery. The upper portion of the conductor 83 is slidable withrespect to a metal plug 61, which is separated from an outer tubularmember 69 by a suitable insulator 1 I, such as Styrol. The plug 51, theinsulator II and the tubular member 69 form a bypass capacitor, which isadjustably mounted in a grounded member 13. This bypass condenser mayhave a large capacity because the problem of blocking does not presentitself in the anode circuit. Also no supplemental ground circuit isrequired because the capacity may be made sufiiciently large toeffectively bypass. If, however, the capacity for any reason is to bekept low, the structure described in connection with the amplifier inputcircuit may be used.

The effective length of the conductor 63 is adjusted by moving thetubular member 69 back and forth within the member 13. The bypasscapacitor formed with the tubular member 89 is fixed in its capacitance,has for practical purposes no leads, and directly and eifectively formsa bypass from the conductor 63 to ground. Thus, the effective length ofthe anode circuit may be adjusted to neutralize capacity reactance withthe amplifier 31. The conductor 63 and the bypass capacitor Bl, H, 99correspond to the inductor l and the capacitor l3, respectively, of Fig.l.

The coupling between the amplifier output circuit and the input to thedetector 75 is a pair of quarter wave concentric lines 11, 19, which areconnected together and are grounded at their junction by a screw 8|. Thescrew 8| acts as the common coupling between the two quarter wavecircuits. In some arrangements, a single quarter Wave line may be madecommon to both circuits, acting, for example, as an autotransformer. Theinner conductor 83 of the concentric lines may be positioned within theouter conductor 85 by an insulated support 81. The lower 11 and upper 19quarter wave lines may be tuned by trimmer capacitors 89, 9| Theamplifier is coupled to the lower line H by the capacitor formed by theplate 59 and insulator 8| which may be fastened to the inner conductor83 as shown. The input to the first detector 15 is made by connectingthe grid lead 93 to the inner conductor 83 at a point of suitableimpedance match. The input tuning may be adjusted by means similar tothat shown for the input of amplifier 31 or by suitably choosing thelength of a conductor 95 connected from the grid to the outer conductor85. The former means is preferred if excessive overloading or blockingeifects are present in the detector. The quarter wave lines H, 19 andthe conductor 95 are equivalent, respectively, to the circuits l1, l9and the inductor 25 of Fig. l.

The local oscillator 9'! is coupled to the detector input circuit byadjusting the mutual coupling between the inner conductor 99 of theoscillator and the upper quarter wave line 19. The outer conductor |8|of the oscillator is slidably mounted on the conductor 85 and spacedtherefrom by an insulating sleeve I93. The insulation is necessary inthe instant arrangement because the outer conductor |0| is at oscillatoranode poten-- tial while the conductor 85 is at ground potential.

A suitable construction for the oscillator is shown in Fig. 3. The innerand outer conductors 99 and |ll| and the insulating sleeve I83correspond to the fragmentary showing in Fig. 2. The outer conductor I!is divided by a ground plate I05. The inner conductor 99 is suitablyfastened, by soldering, brazing, threading or the like, to the groundplate. The oscillator tube I0! is fastened to a socket IE9 or the likewhich may be supported within the conductor I0 I. The grid electrode iscoupled to the ground plate through a capacitor H0. The anode isconnected by a lead III to the inner conductor 99 at a point of suitableimpedance. The cathode is coupled to the inner conductor through lead H3and a capacitor H4. The oscillator frequency may be adjusted over asmall frequency range by a trimmer plate H5 located near the anode leadI II. This trimmer capacitor, and the quarter wave line trimmers 89, 9|have capacities which are very small compared to the total capacity ofthe asssociated lines, whereby the desirable characteristics of theconcentric lines are retained.

Thus I have described an ultra high frequency device in which the inputand output reactances of the associated thermionic tubes may beneutralized by adjustable elements of opposite re actance. Where thebypassing is critical, the capacitors have no leads of appreciablelength. Means are disclosed for establishing points of high or lowimpedance as may be required. The arrangement shown is furthercharacterized by the relative disposition of the component parts whichare positioned to reduce the lengths of leads to a minimum. Finally, thecomponent parts are largely concentric lines in which the losses areextremely low, temperature effects may be corrected, high frequencystability may be obtained and other desirable features, known to thoseskilled in the art, are present. It will be obvious that my inventionmay be applied to ultra high frequency transmitting and receivingdevices. I have chosen to describe the latter merely by way ofillustration.

I claim as my invention:

1. In an ultra high frequency device, a thermionic amplifier includingan input circuit and an output circuit, an oscillator, a first detectorincluding an input circuit, a coupling circuit; said coupling circuitincluding a pair of quarter wave concentric lines, coaxially joined andgrounded at their junction, said amplifier having its output circuitcoupled to one of said quarter wave lines, said detector having itsinput circuit efiectively connected to the other of said quarter wavelines, said oscillator including a concentric line, means for mutuallycoupling the concentric line of said oscillator with one of saidquarterwave lines, and further characerized by an arrangement of saidamplifier and first detector which provide connecting leads of minimumlength to their respective output and input circuits.

2. In an ultra high frequency device of the character of claim 1, meansfor tuning the input and output circuits of said thermionic amplifier.

3. In a device of the character of claim 1, means for tuning the inputcircuit of said amplifier including a rod, and a capacitor slidablymounted on said rod and slidably mounted within a grounded bushing, l

4. In a device of the character of claim 1, means for tuning the outputcircuit of said amplifier comprising a conductor, and a capacitorslidably mounted on said conductor and slidably mounted within agrounded bushing.

5. In a device of the character of claim 1, means for neutralizing thereactance of the input circuit of said amplifier including a conductorconnected directly to said input and to ground by a capacitor adjustablymounted on said conductor and slidably mounted within a groundedbushing, and means for making said ground impedance low.

6. In an ultra high frequency device, a thermionic amplifier includinginput and output circuits, an oscillator, a first detector'including an35 input circuit, a quarter wave concentric line, said amplifier havingits output circuit effectively coupled to said quarter wave line, saiddetector having its input circuit effectively coupled to said quarterWave line, said oscillator including a concentric line, means formutually coupling the concentric line of said oscillator with saidquarter wave line, and further characterized by an arrangement with saidamplifier and said first detector which provides connecting leads ofminimum length to the amplifier input and output circuits and to thedetector input circuit.

ROGERS M. SMITH.

